In recent years, research and development are energetically made on electrophotographic photosensitive members (organic electrophotographic photosensitive members) making use of organic photoconductive materials.
The electrophotographic photosensitive member is basically constituted of a support and a photosensitive layer formed on the support. In the present state of affairs, however, various layers are often formed between the support and the photosensitive layer for the purposes of, e.g., covering any defects of the surface of the support, protecting the photosensitive layer from any electrical breakdown, improving its charging performance, improving the blocking of injection of electric charges from the support into the photosensitive layer, and so forth.
Among such layers formed between the support and the photosensitive layer, a layer containing metal oxide particles is known as the layer formed for the purpose of covering any defects of the surface of the support. The layer containing metal oxide particles commonly has a higher electrical conductivity than a layer not containing any metal oxide particles (e.g., 1.0×108 to 2.0×1013 Ω·cm as initial-stage volume resistivity). Thus, even where it is formed in a large layer thickness, any residual potential at the time of image formation can not easily come to increase, and hence any defects of the support surface can be covered with ease. The covering of defects of the support surface by providing between the support and the photosensitive layer such a layer having a higher electrical conductivity (hereinafter “conductive layer) makes the support surface have a great tolerance for its defects. As the results, this makes the support have a vastly great tolerance for its use, and hence brings an advantage that the electrophotographic photosensitive member can be improved in productivity.
Metal oxide particles used in conductive layers of conventional electrophotographic photosensitive members may include, as an example thereof, titanium oxide particles coated with antimony-doped tin oxide (titanium oxide powder the particle surfaces of which have been coated with tin oxide which contains antimony) as disclosed in Patent Literature 1.
However, it is recently studied from the viewpoint of, e.g., easy availability of materials to make up the conductive layer without use of any antimony, and a technique is disclosed in Patent Literature 2, in which titanium oxide particles coated with oxygen deficient tin oxide are used as metal oxide particles for the conductive layer.
As other metal oxide particles, oxygen deficient tin oxide particles are disclosed in Patent Literature 3. Barium sulfate particles coated with oxygen deficient tin oxide are also disclosed in Patent Literature 4. Barium sulfate particles coated with titanium oxide and tin oxide are still also disclosed in Patent Literature 5.
As a technique aiming at metal oxide particles-containing conductive layers of electrophotographic photosensitive members, an electrophotographic photosensitive member is disclosed in Patent Literature 6, in which a conductive layer (intermediate layer) specifies a relationship between its volume resistivity and temperature/humidity (temperature and relative humidity).